JavaScript RegExp Dot Metacharacter

What Is the Dot .?

In a JavaScript regular expression, an unescaped . is a wildcard: it matches any single character except line terminators. Escape it as \. when you need a literal period.

.     → any one character (not a line break)
\.    → literal period only
.+    → one or more characters (greedy)
.*    → zero or more characters
/s    → dotAll: . also matches newlines

/c.t/ matches "cat", "cut", "c9t"
/\.pdf$/ matches "file.pdf" — not "fileXpdf"

How to Use .

Place the dot where one unknown character should sit, then decide whether you need a literal period or newlines.

1. Write a pattern with . for each unknown single character (for example /c.t/).
2. Escape real periods as \. in versions, decimals, and file extensions.
3. Add a quantifier (+, *, {n}) when you need a run of characters.
4. Add the s flag when the match must cross line breaks.

Pseudocode

pattern has a "." at position p
read next character ch from the string

if ch is a line terminator AND flag "s" is off:
    fail this path

else:
    accept ch as the match for "."
    continue with the rest of the pattern

if pattern used "\." instead:
    accept only when ch is the period character "."

Cheat Sheet

Keep these facts handy while writing wildcard patterns.

Live Preview

Pick a pattern and see whether it matches the sample text with RegExp.prototype.test.

pattern = /c.t/
text = "cat"
pattern.test(text)
→ true

/* "." matches the single character "a" */

JavaScript Examples

Short, copy-ready snippets. Open DevTools Console, or use Try It Yourself for a live editor.

const pattern = /c.t/;

console.log(pattern.test("cat"));   // true
console.log(pattern.test("cut"));   // true
console.log(pattern.test("c9t"));   // true
console.log(pattern.test("cart"));  // false

true
true
true
false

console.log(/version \d+\.\d+/.test("version 2.4")); // true
console.log(/version \d+.\d+/.test("version 2X4"));  // true (wildcard!)

console.log(/\.txt$/.test("notes.txt")); // true
console.log(/\.txt$/.test("notesXtxt")); // false

true
true
true
false

const text = "start\nend";

console.log(/start.end/.test(text));   // false
console.log(/start.end/s.test(text));  // true

const regex = /start.end/s;
console.log(regex.dotAll);             // true

false
true
true

Performance Notes

A lone . is cheap. Cost rises with greedy .+ on long strings and complex patterns. Prefer specific classes (\d, \w) when you do not need “any character.”

Key Takeaways